The idea of coherent states was suggested in QED in the middle of 1960's and in QCD at the end of the 1970's to introduce a realistic definition of initial and final states, where the number of quanta is not determined, unlike the usual approach in perturbation theory. In addition to simply solving conceptual infrared divergences of the S-Matrix, it allows a description of the properties of the QED and QCD radiation to all orders in perturbation theory.In lepton colliders, it gives a precise determination of the line-shape production of the J/ , the Z and the Higgs bosons, while in QCD it allows a realistic description of quark and gluon jets, of the transverse momentum distribution of W, Z and H produced in hadron collisions, and other related quantities.The book consists of a collection of the articles published by the author and his collaborators in about fifty years, with an introduction highlighting the main results of each article and the various links between them.